In the related art, products manufactured by pressing a sheet metal (hereafter, blank), such as sheet iron or sheet aluminum, with a pair of upper and lower concave and convex pressing tools in a predetermined shape, are often used for automotive parts or home appliances. Recently, it is common to see higher-strength materials being used to reduce the thickness of materials in order to reduce the weight of products. On the other hand, since a forming-reacting force increases when pressing a high-strength material, the die or the pressing device elastically deforms, such that the material cannot be machined with predetermined dimensions in some cases.
In more detail, in a forming process, a blank is held by a fixed lower pressing tool (die), a wrinkle-pressing tool (blank holder) is hydraulically operated to apply pressure, and then an upper pressing tool (punch) draws the blank while traveling down to a predetermined depth. With an insufficient wrinkle-pressing pressure (blank hold pressure), the blank wrinkles, whereas with too high a wrinkle-pressing pressure, the blank cracks. Therefore, it is important to obtain a good product to apply an optimal blank hold pressure and, recently, forming simulation using the Finite Element Method is actively used to examine the optimal blank hold conditions.
In a common forming simulation, the contact status between the die and the blank is sequentially determined, on the assumption that the die is a rigid body and the blank is a deformable body. On the basis of this determination, the deforming process of the blank is calculated step by step.
Meanwhile, in practical forming, elastic deformation or poor parallelism of the up-down matching surfaces is caused by various factors, such as the degree of precision in positioning of the punch and die (the up-down matching surface), the pressing point of the blank holder (position of a cushion pin), rigidity of the press and die, and deforming resistance of the blank or the plate thickness. Therefore, it is necessary to consider the elastic deformation of the die or the parallelism of the up-down matching surface.
Non-patent Document 1 discloses a technology for modeling the blank holder into a deformable body and performing coupled analysis on the elastic deformation of the die and forming of the workpiece.
Further, Patent Document 1 and Patent Document 2 disclose a method of performing an elastic deformation simulation of the die with an input that is a nodal reacting force obtained from a forming simulation on the assumption that the die is a rigid body, and performing recalculation by reflecting the distribution of deflection obtained from the simulation to the die shape in the forming simulation.